The outstanding properties of graphene have been established on pristine samples in idealized conditions. However, for most applications, graphene needs to be chemically functionalized in a manner that either preserves its intrinsic properties or modifies its properties in a manner that enhances functionality. Towards these ends, several noncovalent chemistries have been demonstrated and characterized at the molecular scale with ultra-high vacuum scanning tunneling microscopy including 3,4,9,10-perylenetetracarboxylic dianhydride and 10,12 pentacosadiynoic acid.  These self-assembled monolayers are shown to be effective atomic layer deposition seeding layers for dielectrics (e.g., Al₂O₃, HfO₂, and ZnO), which allows for substantial improvements in the uniformity and reliability of metal-oxide-graphene electronic devices. On the other hand, covalent modification schemes based on free radical chemistries allow for more fundamental changes to the electronic and chemical properties of graphene. In particular, atomic oxygen has been established as an effective method for homogeneously and reversibly functionalizing graphene with epoxide groups. In addition to chemically doping graphene, epoxidation yields local modification of the graphene bandstructure and provides pathways for further chemical functionalization, thereby expanding the suite of chemically modified graphene heterostructures. Finally, this talk will conclude with ongoing work in our laboratory to extend the chemical modification strategies for graphene to other two-dimensional materials including ultrathin silicon [1,2], black phosphorus [3,4], and transition metal dichalcogenides [5].

[1] A. J. Mannix, B. Kiraly, B. L. Fisher, M. C. Hersam, and N. P. Guisinger, “Silicon growth at the two-dimensional limit on Ag(111),” ACS Nano, 8, 7538 (2014).

[2] B. Kiraly, A. J. Mannix, M. C. Hersam, and N. P. Guisinger, “Graphene-silicon heterostructures at the two-dimensional limit,” Chem. Mater., 27, 6085 (2015).

[3] J. D. Wood, S. A. Wells, D. Jariwala, K.-S. Chen, E. Cho, V. K. Sangwan, X. Liu, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Effective passivation of exfoliated black phosphorus transistors against ambient degradation,” Nano Lett., 14, 6964 (2014).

[4] X. Liu, J. D. Wood, K.-S. Chen, E. Cho, and M. C. Hersam, “In situ thermal decomposition of exfoliated two-dimensional black phosphorus,” J. Phys. Chem. Lett., 6, 773 (2015).

[5] X. Liu, I. Balla, H. Bergeron, G. P. Campbell, M. J. Bedzyk, and M. C. Hersam, “Rotationally commensurate growth of MoS₂ on epitaxial graphene,” ACS Nano, DOI: 10.1021/acsnano.5b06398 (2015).